1. Field of the Invention
The present invention relates generally to a modification of an refrigeration apparatus, for example suitable for employment in an air-conditioning device for automotive use, and more particularly, to a modification of an evaporator in a refrigeration apparatus for the purpose of performance enhancement.
2. Description of the Related Art
An example provided in Japanese Patent Application Laid-open No. Hei 5-18635 exists as a prior example intended to enhance evaporator performance in a refrigeration apparatus of this type. This prior art disposes a gas-liquid separation chamber to separate gas-phase and liquid-phase refrigerant on a core portion side end portion of a laminate type evaporator composed by laminating flat tubing and corrugated fins, providing in this gas-liquid separation chamber an inlet chamber to which a refrigerant inlet pipe is connected and an outlet chamber to which a refrigerant outlet pipe is connected, disposing an inlet side tank portion communicated with an inlet tank of the core portion on a bottom portion of the inlet chamber, disposing an outlet side tank portion communicated with an outlet tank of the core portion on a bottom portion of the outlet chamber, and further structured to cause the inlet chamber and the outlet chamber to be communicated by a bypass passage portion at an uppermost portion thereof.
By means of this, refrigerant of which the pressure has been reduced by a pressure-reducing means of an expansion valve or the like to assume a gas-liquid two-phase state is separated in a vertical direction by means of specific gravity differential in the gas-liquid separation chamber; liquid-phase refrigerant with high specific gravity is caused to flow from the inlet chamber bottom portion through the inlet side tank portion and into an inlet tank of the core portion, such that the liquid-phase refrigerant is distributed uniformly of this inlet tank to multiple flat tubing. Meanwhile, in the inlet chamber of the gas-liquid separation chamber, gas-phase refrigerant with low specific gravity shifts to the upper side, and passes through the bypass passage portion of the uppermost portion to flow directly into (bypass) the outlet chamber. Accordingly, gas-phase refrigerant which has exchanged heat with blown air for air-conditioning use or the like and evaporated in the flat tubing passes through the core portion outlet tank and flows into the outlet chamber. Consequently, gas-phase refrigerant which has evaporated in the core portion and gas-phase refrigerant which has bypassed from the gas-liquid separation chamber is mixed in this outlet chamber, is discharged externally from the outlet pipe, and is taken into the compressor.
As an incidental comment, according to the foregoing conventional device, if gas-phase refrigerant can be separated sufficiently in the gas-liquid separation chamber, this separated gas-phase refrigerant can be distributed uniformly to the respective tubing of the core portion, and so effective utilization for the purpose of heat exchange with the entirety of the core portion without generating excessive or insufficient refrigerant among the multiple tubing is possible.
However, specific experimentation and investigation by the inventors with regard to the foregoing conventional device revealed the occurrence of the problems that will be described hereinafter.
To wit, firstly, because gas-phase refrigerant which has been separated in the gas-liquid separation chamber utilizing the specific gravity differential of gas-phase and liquid-phase refrigerant is caused to flow into the core portion inlet tank without change, at times such as during a summer period when the cooling load is large, in a case of R134a refrigerant, high pressure (i.e., pressure of the high-pressure circuit from the compressor discharge side to the pressure-reducing means inlet side of the refrigeration apparatus) assumes a high pressure of about 15 kg/cm.sup.2, and as a result thereof refrigerant downstream of the pressure-reducing means (evaporator inlet) is subsequent to pressure reduction, and so the degree of dryness thereof becomes large, a large quantity of gas is generated, and the proportion of gas-phase refrigerant in terms of the weight ratio reaches 40%. For this reason, gas-phase and liquid-phase refrigerant cannot be separated sufficiently in the gas-liquid separation chamber, and refrigerant flows into the core portion in a state wherein gas-phase refrigerant is intermixed with the liquid-phase refrigerant. It was discovered that, by means of this, the distribution of liquid-phase refrigerant to the respective tubing in the core portion becomes nonuniform, leading to a drop in evaporator performance.
Secondly, in a case where a temperature-operating type expansion valve is used as a pressure-reducing means, a temperature-sensing tube is disposed on a downstream side of the refrigerant outlet pipe of the evaporator, and so the temperature of refrigerant in which is mixed superheated gas-phase refrigerant evaporated in the core portion and saturated gas-phase refrigerant bypassed from the foregoing gas-liquid separation chamber is necessarily detected. As a result of this, a temperature lower than the actual temperature of the superheated gas-phase refrigerant of the evaporator outlet by an amount corresponding to the saturated gas-phase refrigerant comes to be detected, and the problem occurs wherein the expansion valve cannot optimally regulate refrigerant flow to the evaporator. Actually, it was discovered that the expansion valve tends to close, leading to the problem of a drop in evaporator capacity.
Furthermore, when cooling load is small and the degree of dryness of refrigerant downstream of the expansion valve is small, liquid-phase refrigerant comes to be intermixed with gas-phase refrigerant separated in the gas-liquid separation chamber and bypassed, and so the detected temperature of the temperature-sensing tube drops further, and as a result thereof the above-described problem becomes more marked.